A protective device is described in German Patent Application No. 1 97 46 410.6, in which, in the case of electrostatic discharge (ESD), a vertically arranged transistor diode is switched through by a lateral punch-through effect. In the protective device described there, however, the snap-back voltage, i.e. the minimum voltage which has to be present between collector and emitter after breakdown so that the diode remains switched through, is limited to a value which is predetermined by the thickness of the layer of the semiconductor system's surface area, on which the protective device is mounted.